Partition Function of N Particles: Is Z=(Z_1)^N?

In summary, for a system of N independent particles, the partition function for the N particle system is not equal to the product of the partition function for one particle raised to the power of N. This is true for a classical system, but not for a quantum system due to the Pauli exclusion principle. In the quantum case, the grand-partition function is usually used to calculate the partition function.
  • #1
Pacopag
197
4

Homework Statement


If we have a system of N independent particles and the partition function for one particle is Z_1, then is the partition function for the N particle system Z=(Z_1)^N?


Homework Equations





The Attempt at a Solution


I'm pretty sure that this is true for a classical system, but I'm not sure if it's true for a quantum system. Does the Pauli exclusion principle spoil this somehow?
 
Physics news on Phys.org
  • #2
Even without quantum considerations, you end up with over counting if the particles are identical. See Gibb's Paradox.
 
  • #3
Right. Sorry, I meant to write
[tex]Z={1\over {N!}}(Z_1)^N[/tex]
Does that take care of over counting?
What about the quantum case?
 
  • #4
It is not true for the quantum case. The quantum case is easier handled via grand-partition function.
 
  • #5
So in the quantum case, if we want to use the canonical ensemble, we have to calculate the whole partition function all in one shot?
 
  • #6
Yep. But like I said, usually, you calculate the grand-partition function (which factorises neatly into a function of single particle states).
 

1. What is the partition function of N particles?

The partition function of N particles is a mathematical concept used in statistical mechanics to describe the energy distribution of a system with N particles. It is denoted by Z and is a sum of all possible energy states of the system.

2. How is the partition function of N particles calculated?

The partition function of N particles can be calculated using the formula Z = ∑e^(-E_i/kT), where E_i is the energy of each possible state of the system, k is the Boltzmann constant, and T is the temperature.

3. What is the significance of the partition function in statistical mechanics?

The partition function is a crucial concept in statistical mechanics as it allows us to calculate the thermodynamic properties of a system, such as its energy, entropy, and free energy. It also provides a way to connect the microscopic behavior of particles to macroscopic observations.

4. Can the partition function of N particles be written as Z=(Z_1)^N?

Yes, the partition function of N particles can be written as Z=(Z_1)^N, where Z_1 is the partition function of a single particle. This is known as the canonical ensemble and is used to describe systems with fixed particle number, temperature, and volume.

5. How does the partition function change with an increase in the number of particles?

The partition function of N particles increases exponentially with an increase in the number of particles. This is because the number of possible energy states also increases with the number of particles, leading to a larger number of terms in the summation formula.

Similar threads

  • Advanced Physics Homework Help
Replies
1
Views
736
  • Advanced Physics Homework Help
Replies
1
Views
571
  • Advanced Physics Homework Help
Replies
1
Views
2K
  • Advanced Physics Homework Help
Replies
1
Views
1K
  • Advanced Physics Homework Help
Replies
5
Views
1K
  • Other Physics Topics
Replies
1
Views
1K
  • Advanced Physics Homework Help
Replies
3
Views
1K
  • Advanced Physics Homework Help
Replies
2
Views
3K
  • Advanced Physics Homework Help
Replies
6
Views
4K
  • Quantum Physics
Replies
9
Views
780
Back
Top